使用内存映射提高BufferedRandoAccessFile性能（测试可用）

　　网上搜索了代码：

• 使用byte数组缓冲的，不能用。
• 如何使用内存映射，没有可用代码。

　　只好自己研究，先从简单的开始。目前还将就着能用。

package quantum6;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;


public final class BufferedRandomAccessFile extends RandomAccessFile
{
    private static final  int BUFFER_SIZE = 1024*1024;
    
    
    private String filePath;

    private int outSize = BUFFER_SIZE;

    private MappedByteBuffer mbbi;
    private MappedByteBuffer mbbo;
    
    public BufferedRandomAccessFile(File file, String mode) throws FileNotFoundException
    {
        this(file, mode, file.length());
    }
    
    public BufferedRandomAccessFile(File file, String mode, long size) throws FileNotFoundException
    {
        super(file, mode);
        filePath = file.getAbsolutePath();
        try
        {
            if (mode.contains("r"))
            {
                FileChannel fci = getChannel();
                mbbi = fci.map(FileChannel.MapMode.READ_ONLY,  0, size);
            }
            if (mode.contains("w"))
            {
                FileChannel fco = getChannel();
                mbbo = fco.map(FileChannel.MapMode.READ_WRITE, 0, size);
            }

            init(file.length());
        }
        catch (IOException e)
        {
            throw new FileNotFoundException();
        }
    }
    
    private void init(long size) throws IOException
    {
        /*
        bufferOffsetLeft  = 0;
        bufferOffsetRight = size;
        bufferPointer = 0;
        
        bufferSize = (int)(size > BUFFER_SIZE ? size : BUFFER_SIZE);
        bufferData = new byte[bufferSize];
        */
    }

    public String getPath()
    {
        return filePath;
    }
    
    @Override
    public void seek(long pos) throws IOException
    {
        mbbi.position((int)pos);
    }
    
    @Override
    public int read() throws IOException
    {
        return mbbi.get();
    }
    
    @Override
    public int read(byte[] b) throws IOException
    {
        return this.read(b, 0, b.length);
    }
    
    @Override
    public int read(byte[] b, int off, int len) throws IOException
    {
        int left = mbbi.remaining();
        mbbi.get(b, off, len);
        return (mbbi.remaining() - left);
    }
    
    private void checkWriteBuffer()  throws IOException
    {
        if (mbbo == null || !mbbo.hasRemaining())
        {
            outSize += BUFFER_SIZE;
            FileChannel fco = getChannel();
            mbbo = fco.map(FileChannel.MapMode.READ_WRITE, 0, outSize);
        }
    }

    @Override
    public void write(int b) throws IOException
    {
        checkWriteBuffer();
        mbbo.put((byte)b);
    }
    
    @Override
    public void write(byte[] b) throws IOException
    {
        this.write(b, 0, b.length);
    }
    
    @Override
    public void write(byte[] b, int off, int len) throws IOException
    {
        checkWriteBuffer();
        mbbo.put(b, off, len);
    }

}